As a former trademark examining attorney for the U.S. Patent and Trademark Office and founder of The Trademark Company I am often asked for suggestions on how to select a great trademark by our start-up business customers.  The response is always the same, "It depends on what you want out of your trademark."
There are two schools of thought in selecting a great trademark that every new business must consider. On one hand do you want to use a completely coined name? Something that no one has ever heard of such as Google or eBay. 
On the other, do you want a trademark that creates instant interest in the product or service because it tells your prospective customers what you provide and what they’ll get (e.g., FROSTED MINI WHEATS for breakfast cereals, VISION CENTER for retail store services featuring eyewear).
Both schools of thought have their benefits. Both also have their detriments. 
Which should you choose? Like I said above, it depends upon what you are looking for out of your trademark. Coined trademarks, those that are completely made up, are the strongest form of trademarks and, in theory, the easiest to protect (e.g., Google, eBay, Hulu, etc.). But beware, although easier to protect, such trademarks do not tell the consumer what you do or what goods or services you provide. As such, if you intend to coin your own trademark be ready to spend more to promote your brand name as there will not be instant recognition by consumers of what you do or provide.
Descriptive trademarks, on the other hand, provide the owner with instant recognition for what their brand does (e.g., NEW YORK PIZZERIA). This comes at a cost, however. Descriptive trademarks are very hard to enforce and, as a result, may not provide the owner the ability to enforce their trademarks (e.g., the owner of NEW YORK PIZZERIA, more likely than not, cannot stop someone else from using NEW YORK CITY PIZZERIA even though the trademarks are very similar). As such, if you are looking to adopt a trademark that instantly drums up interest in your goods or services and will cost less to brand adopting a descriptive trademark may be best for you. You simply need to know that the rights you will acquire in any such trademark may never entitle you to exclude others from the use of similar trademarks.
So in the end how do you select a great trademark? It depends. What are you looking for?